Format: ORAL

Lizo E. Masters1,2, Paulina Tomaszewska1,3, Trude Schwarzacher1,4, Alexandre R. Zuntini2, Pat Heslop-Harrison1,4, Maria Vorontsova2

1University of Leicester, Leicester, United Kingdom 2 Royal Botanic Gardens, Kew, Richmond, United Kingdom 3University of Wroclaw, Wroclaw, Poland 4South China Botanical Garden, Guangzhou, China

African grasses in the genus Urochloa (Brachiaria)have been recognised for their forage crop potential as early as the 18th century. Three closely related African species (U. brizantha, U. decumbens, and U. ruziziensis) dominate Urochloa breeding and are hybridizied to produce the worlds most commercially important tropical forage cultivars. These three grasses form a naturally occurring species complex characterised by diverse ploidy levels, overlapping morphologies, and sexual and asexual reproduction. The reticulate evolution of U. brizantha, U. decumbens and U. ruziziensis, and their phylogenetic relations within Urochloa remain unclear. Elucidating this history will greatly benefit future breeding projects. We inferred a species level phylogeny for Urochloa using target enrichment and RNA-seq data from Kew Herbarium and Centro Internacional de Agricultura Tropical (CIAT) accessions. Additionally, we estimated ancestral states for important forage traits using our phylogeny. Finally, we investigated reticulate evolution in U. brizantha, U. decumbens, U. ruziziensis and their closest wild relatives using phylogenetic networks and fluorescent in-situ hybridization (FISH). Our analysis revealed the independent evolution of five forage clades across Urochloa.Urochloa brizantha, U. decumbens, and U. ruziziensis form a well-supported clade with two wild relatives, U. eminii and U. oligobrachiata. Phylogenomic networks and FISH analysis confirm that U. brizantha and polyploid U. decumbens are hybrid species that share at least one parental lineage. Further, diploid U. decumbens and polyploid U. decumbens belong to separate lineages, which is supported by morphological data, chloroplast phylogenies, and previous population genetic and cytological work. We found evidence of reticulate evolution between polyploid U. decumbens and the lineage containing diploid U. decumbens and U. ruziziensis.The reticulate evolution of U. brizantha is more complex as diploids and polyploids share a single origin. Our study demonstrates that multiple lines of evidence (morphological, phylogenetic, cytological) are required to disentangle highly reticulate species complexes.